1. Field of the Invention
The present invention relates to an arithmetic processing algorithm for flight velocity vector measurement of a wide velocity range that extends from low velocities to supersonic velocities and to a system using said algorithm.
2. Description of the Related Art
The present applicant previously invented and obtained a patent for (U.S. Pat. No. 5,423,209; Japanese Patent No. 2913005) a flight velocity vector measurement system using a square truncated pyramid-shape five-hole Pitot probe as in FIG. 6. FIG. A is a front view. FIG. B is a partial side sectional view. As in FIG. A, a group of pressure holes having a total pressure hole in the center thereof is provided on each of the four slanted sides of the pyramid shape. The patented invention is a flight velocity vector detection system using a multi-side truncated pyramid shape Pitot probe wherein an extreme end portion has a multi-side truncated pyramid shape, a shield hole is provided at the apex thereof, a total pressure tube of a smaller diameter than that of the shield hole is secured at a position by a predetermined length determined by a relationship with the diameter of the shield hole from the extreme end of the shield hole; wherein pressure information detected by said multi-side truncated pyramid shape Pitot probe on each side thereof are positioned pressure holes is input to a velocity vector arithmetic processor to convert said information into electronic signals, which are processed using pressure coefficients of the pressure holes of said probe with respect to velocity vector, said pressure coefficients being stored in advance in a memory, to calculate flight velocity vector (V, xcex1, xcex2) with respect to the probe axis from the pressure information and air density; wherein an output of an attitude azimuth reference device is input to said velocity vector arithmetic processor and information from the attitude azimuth reference device is connected with flight velocity vector information with respect to said airframe axis to calculate flight velocity vector. Adoption of such a configuration enables a single square truncated pyramid shape Pitot probe and an arithmetic processor to perform the respective functions of a conventional airspeed indicator, altimeter, rate of climb indicator, Mach meter, and yaw meter, thereby making it possible to reduce the number of detection devices; to connect the various information and output and display said information; and to provide a pilot with highly reliable atmospheric information. Furthermore, a limited effect of pressure coefficients caused by variation in velocity eliminates the need to perform complex correction, making it possible to obtain velocity vector information with good accuracy and over a wide angular range and facilitating installation, without the need for an advanced computer, in a wide range of aircraft, from ordinary aircraft, including helicopters and other vertical takeoff and landing aircraft, to supersonic aircraft that are accompanied by shock waves. In addition, [the patented invention] is a groundbreaking invention offering many superior effects, namely, being less influenced by the pressure coefficients caused by variation of velocity of those pressure holes that detect wind direction, requiring no complicated correction, being able to obtain velocity vector information with good accuracy and over a wide angular range, and posing no likelihood of defective measurement due to clogging, vibrations and the like.
Arithmetic processing method""s concerning Mach number M (or velocity V) stored in ROM form and used in an arithmetic processor for a flight velocity vector measurement system that uses a square truncated pyramid-shape five-hole Pitot probe comprise (1.) those in which said five-hole probe is not subjected to compression and which are suitable for low-velocity ranges not requiring high-speed arithmetic processing and (2.) those suitable for a wide range of velocities that extends from low velocities to supersonic velocities accompanied by shock waves. The former, namely (1.) arithmetic processing for low-velocity ranges in which said five-hole probe is not subjected to compression, is a processing technology wherein the Newton-Raphson method (xe2x80x9cN-R methodxe2x80x9d) is used and wherein three parameters comprising attack angle xcex1, sideslip angle xcex2, and velocity (dynamic pressure q) are determined, by repeated calculation, using pressure calibration coefficients concerning attack angle, sideslip angle, and velocity calculated in advance. Said technology is disclosed in the Specifications of the said patented invention and has been implemented in the HOPE Automatic Landing Flight Experiment (ALFLEX) demonstration vehicle and in NAL experimental vehicles.
Regarding the latter, namely (2.) arithmetic processing methods for a wide range of velocities that extends from low-velocity flight to supersonic-velocity flight in which said five-hole probe is subjected to shock waves, flight velocity vector arithmetic processing equations that were also developed by the present applicant and in which five items of pressure information are used as basic data and Mach number M is first determined by some processing method and then used determine angle have been presented (U.S. Pat. No. 2884502, xe2x80x9cWide Velocity Range Flight Velocity Vector Measurement System Using a Square Truncated Pyramid-Shape Five-Hole Probexe2x80x9d). This technology has been used in airflow measurement in supersonic wind tunnels.
The flight velocity vector calculation methods for the aforesaid (2.) comprise two methods. One is a system wherein a Mach number equation and angle equations are solved directly in third-order polynomial approximation equations for each segmented velocity range; the other, a lookup table system that omits the solution of a third-order equation for intermediate calculation of the Mach number and wherein Mach number is read directly from a Mach number table created in advance by calculating Mach number M from airflow angle pressure coefficient and Mach pressure coefficients determined in advance. Within the former system for solving Mach number M and angles with third-order equations, Mach number calculation, wherein angle to airflow pressure coefficient Cxcex3 is obtained in advance by further processing Mach pressure coefficient CM, which is obtained by making a pressure difference between a total pressure and average pressure of four holes in the square truncated pyramid surfaces obtained by processing the five items of pressure information detected by said five-hole probe nondimensional according to said total pressure, and wherein pressure coefficients Cxcex1 and Cxcex2 are also obtained in advance by making a vertical pressure difference and transverse pressure difference among the four holes in the square truncated pyramid surfaces nondimensional according to total pressure, is specified using pressure calibration coefficients determined in advance for each velocity range in conjunction with determination of segmented velocity ranges, said velocity ranges being determined from the aforesaid pressure coefficient CM, and the aforesaid angle to airflow pressure coefficient Cxcex3. Mach number M is arrived at by solving said third-order equations for each velocity region to determine an appropriate root. Angles are arrived at by similarly solving a third-order arithmetic processing equation concerning angle xcex1 and angle xcex2 using aforesaid pressure coefficients Cxcex1 and Cxcex2 and the pressure calibration coefficient corresponding to the angle. The arithmetic processing equation used to calculate Mach number, angle xcex1, and angle xcex2 are all third-order equations, each having three roots (with said roots comprising either three real roots or one real root and two imaginary roots), and so selection of an appropriate root entails using complicated determination methods.
The other method, namely the lookup table method, is a method wherein, without using a third-order equation in Mach number determination, Mach pressure coefficient CM and angle to airflow pressure coefficient Cxcex3 are first obtained from preset Mach number M, which can be obtained during calibration wind testing in which the aforesaid five-hole probe is placed in a wind tunnel, and from five items of pressure information obtained for each setting of the probe""s angle xcex1 and angle xcex2 (i.e., the probe""s preset angle value for the airflow axis); wherein, using three parameters comprising said Mach number M, angle to airflow pressure coefficient Cxcex3, and Mach pressure coefficient CM, a lookup table (FIG. 5) that graphs Mach number M on an orthogonal plane having angle to airflow coefficient Cxcex3 as its horizontal axis and Mach pressure number CM as its vertical axis is comprised; and wherein Mach number M can be directly determined by applying the aforesaid angle to airflow pressure coefficient Cxcex3 and Mach pressure coefficient CM. This lookup table, as shown in FIG. 5, is divided into separate sections for each velocity range. Furthermore, attack angle xcex1 and sideslip angle xcex2, which are airflow angles, are calculated with a method wherein a third-order equation concerning attack angle xcex1 is established using a Mach number M that is obtainable from the lookup table, an attack angle pressure calibration coefficient Aij calculated in advance, and the aforesaid Mach pressure coefficient Cxcex1; wherein a third-order equation concerning sideslip angle xcex2 is similarly established in the aforesaid Mach number M, a sideslip angle xcex2 pressure calibration coefficient Bij calculated in advance, and the aforesaid Mach pressure coefficient Cxcex2; and wherein said third-order equations are solved directly to select the appropriate root, thereby determining attack angle a and sideslip angle xcex2. This method, although simplifying calculation of Mach number M by use of a table system, requires solving and interpreting of third-order equations in the calculation of airflow angles of attack angle xcex1 and sideslip angle xcex2.
Generally, an arithmetic processor in a flight velocity vector measurement system that is loaded on aircraft capable of flying at wide range of velocities, from low velocities to supersonic velocities, has a configuration that includes a pressure converter, CPU, ROM, interface and the like and must be compact, lightweight, and resistant to electromagnetic environments and have high accuracy in the form of high reliability and sophisticated arithmetic processing capabilities. Furthermore, arithmetic processing signals must be obtainable in real time so as to be introduced into externally connected avionics and flight control devices and thereby facilitating active control with respect to atmospheric disturbance. Hence, arithmetic processing requiring solving of third-order equations by an existing arithmetic processor in the aforesaid flight velocity vector measurement system is inadequate, and a method that makes possible new, high-accuracy, high-speed arithmetic processing is required. Incidentally, application of the aforesaid technology (1.), as said technology essentially uses the N-R method, requires increasing the number of repeated calculations in order to increase measurement accuracy and is an unsuitable method with respect to securing a high update rate because of the difficulty of high-speed processing. In addition, technology (2.), as already stated, although simplifying calculation of Mach number M by using a table system, requires solving of third-order equations to calculate airflow angles xcex1 and xcex2. In particular, limitations exist with respect to direct solving of the polynomial approximation equation (third-order equation) used to increase accuracy, in that because [said equation], being a third-order equation, has three roots (with said roots comprising either three real roots or one real root and two imaginary roots), determination of the appropriate root requires a complicated determination algorithm, whereas loosening of criteria leads to problems with measurement accuracy. Thus, limitations exist with respect to obtaining high accuracy and a high update rate. Therefore, a new arithmetic processing method capable of ensuring high reliability, high accuracy, and a high update rate has been desired for flight velocity vector measurement systems applicable even in supersonic aircraft.
An object of the present invention is to solve the above-mentioned problems, namely, to provide an arithmetic processing algorithm that, in a wide velocity range that extends from low velocities to supersonic velocities and in a flight velocity vector measurement system employing a square truncated pyramid-shape five-hole Pitot probe, is capable of arithmetically processing, with high accuracy and high update rate, a flight velocity vector that indicates velocity extent and airflow angle and a static pressure that indicates altitude; and to provide a flight vector measurement system that, being compact, lightweight, and resistant to electromagnetic environments and having high accuracy in the form of high reliability and sophisticated arithmetic processing capabilities, is capable of arithmetically processing the aforesaid algorithm with high accuracy and a high update rate in an arithmetic processing apparatus.
The arithmetic processing method of the present invention that resolves the above-mentioned problems expresses approximation equations that determine attack angle xcex1 and sideslip angle xcex2 in the form of third-order equations concerning attack angle pressure coefficient Cxcex1 and sideslip angle pressure coefficient Cxcex2, which are known numbers; is expressed the form of a polynomial equation concerning Mach number M that is capable of instantly calculating said coefficients from a lookup table; enables coefficient calculations in said polynomial equation and calculation of attack angle xcex1 and sideslip angle xcex2 to be performed as simple calculations by specifying and applying a known number into the approximation equation without solving a third-order equation as is done conventionally, with calibration coefficients that form the basis of coefficient calculation with the polynomial equation first being stored in memory in advance as a table for each wide velocity range on the basis of wind tunnel testing; enables a Mach number to be calculated instantly from a lookup table by specifying Mach pressure coefficient CM and angle to airflow pressure coefficient Cxcex3; permits wide velocity range flight velocity vector measurement with a high update rate; and is capable of real time response in flight control as demanded by aircraft.